A basic study has been conducted to visualize the inner structure in a dense scattering medium such as a living body. The following results were obtained through theoretical and experimental investigations.1. With the nearーinfrared light (wavelength 700-900 nm, optical power 1 W), the transillumination image of a human palm could be observed. In the image, the skeletal structure was hardly recognized, but blood vessels were clearly observed.2. The visualized depth was measured to be several millimeters from the skin surface. Thus, it was found that the transmission of light was enough but that deep structure of a living body could not be visualized with conventional techniques. To visualize the structure, the weak straight light has to be extracted from the strong scattered light.3. A new technique was developed which suppresses the scattered light based on the differential and collimation methods.4. It was found that the scattered light was greatly suppressed by the use of short optical pulses (10-30 psec) and a streak camera. This technique was proved to be useful with a living tissue, as well.5. The feasibility of an optical CT was tested. The crosssectional shapes of the three posts immersed in a milk solution were clearly identified in the image obtained with the newly developed technique.6. An experimental system of trans-body imaging was developed using highーintensity light sources and sensitive detectors. With the system, the movements of internal organs of experimental animals could be observed.7. The trans-body images were obtained in different wavelengths. The images were processed, and the distribution of oxygenation-changes in a living tissue was visualized.